铁（Fe）是生物生长所必需的微量元素，在海洋浮游植物的光合作用、呼吸作用和固氮过程中起着举足轻重的作用。在各种形态Fe中，能被浮游植物吸收利用的主要是溶解态Fe，特别是溶解态Fe(II)，但是胶体态和颗粒态Fe 在一定条件下亦能转变成溶解态，是浮游植物可利用的潜在Fe 源。已有的研究还发现一些藻类可以吸收并利用胶体态Fe，甚至某些颗粒态Fe。这些具有生物（潜在）有效性的Fe 一般用可溶态Fe（dissolvable Fe，通常表示为Fea）表征。由于河口及近岸海域靠近陆地和陆架沉积物输入源，溶解态和颗粒态Fe 浓度的时空变化显著，而高浓度的溶解态和颗粒态Fe 可能有利于某些微藻的生长，甚至引发赤潮。
为实现大范围实时观测河口和近岸海域的不同氧化还原形态Fea 的浓度及其分布，袁东星教授课题组开发了双载流-反相流动注射-长光程分光光度法检测系统（dual carriers-reverse flow injection-LWCC-spectrophotometric detection system, DC-rFIA-LWCC），并成功地与拖曳走航式采样技术联用，首次实现了纳摩尔级浓度Fe(II)和Fe(II+III)的走航同时观测。在2009年973 计划项目“中国近海碳收支、调控机理及生态效应研究（CHOICE-C）”夏季航次中，该走航观测系统在“东方红2”科考船上进行了海试实验，获得了长江口及东海表层海水中现场可溶态Fe(II)和Fe(II+III)（即Fea(II)和Fea(II+III)）的浓度数据及其分布。结果表明，Fea(II)和Fea(II+III)的浓度与盐度显著负相关；受长江冲淡水控制的表层海水具有较高浓度的Fea(II)和Fea(II+III)，且随盐度的升高而迅速降低；Fea(II)在Fea(II+III)中所占的比例呈现明显的区域差异，其在长江口附近（盐度<30）可达50%以上，而在盐度高于30 的区域，仅约为19%，与开阔大洋的水平相当。该成果有助于研究河口和近岸Fe的生物地球化学过程，可为探索近岸Fe向远洋的输送机制提供参考。该成果发表在Environmental Science & Technology上：Yongming Huang, Dongxing Yuan*, Yong Zhu, and Sichao Feng. Environ. Sci. Technol., 2015, 49(6), 3619-3627.
Abstract:
An automated, shipboard-use system was developed for real-time speciation of iron in coastal surface waters. It comprised a towed Fish underway sampler and a modified reverse flow injection analysis system with a liquid waveguide capillary flow cell–spectrophotometric detection device. The detection was based on the reaction between ferrozine and Fe(II). The detection limits of 0.3 and 0.7 nM were achieved for Fe(II) and Fe(II+III), together with their respective dynamic linear ranges of 0.5–250 and 0.9–250 nM. The system was successfully deployed and run consecutively for about 1 week during a cruise in August 2009 to the East China Sea off the Changjiang Estuary. The distribution of operationally defined field dissolvable Fe(II) and Fe(II+III) (expressed as Fea(II) and Fea(II+III)) in these areas was obtained, which showed that both Fea(II) and Fea(II+III) concentrations decreased with salinity when there were relatively high Fea(II) concentrations (up to about 120 nM) near shore. A distinct distribution of Fea(II) to Fea(II+III) ratios was also revealed, with a ratio of 0.58 in the water off Changjiang Estuary and 0.19 in the open ocean.
Link to full text: http://pubs.acs.org/doi/full/10.1021/es505138f.
